Thrombus associated diseases are vascular conditions that develop due to the presence of a clot. Such diseases are a major cause of mortality, and therefore developing thrombus-specific diagnosis, treatment, and detection methodologies and reagents is of great clinical importance. Pulmonary embolism (PE), deep-vein thrombosis (DVT), stroke, and atherosclerosis are examples of thrombus-associated diseases.
DVT is a condition in which blood clots form in the deep blood vessels of the legs and groin. These clots can block the flow of blood from the legs back to the heart. Sometimes, a piece of a clot is detached and carried by the bloodstream through the heart to a blood vessel, where it lodges and reduces, or blocks, the flow of blood to a vascular tissue. This is called an embolism. If such a clot lodges in pulmonary blood vessel it can be fatal.
In the United States alone an estimated 600,000 patients suffer from PE's each year. In approximately 378,000 of these patients, PE goes undetected, and approximately 114,000 of these patients later die due to complications associated with the disease. This high mortality is partly due to the absence of clinical symptoms in many cases and to the significant limitations associated with currently available methods of investigation and detection.
Fibrin is also associated with various cancers. The existence of heterogeneous pattern of fibrin/fibrinogen deposition in various tumor types is a concept supported by a substantial body of correlative and indirect evidence suggesting that fibrin/fibrinogen is important in tumor stoma formation (see, for instance: Costantini V, Zacharski L R. Fibrin and cancer. Thromb Haemost. 1993; 69:406; Dvorak H F. Thrombosis and cancer. Hum Pathol. 1987; 18:275; Dvorak H F, Nagy J A, Berse B, et al. Vascular permeability factor, fibrin, and the pathogenesis of tumor stroma formation, Ann N Y Acad. Sci. 1992; 667:101; Cavanagh P G, Sloane B F, Honn K V. Role of the coagulation system in tumor-cell-induced platelet aggregation and metastasis. Hemostasis. 1988; 18:37 and Bardos H, Molnar P, Csecsei G, Adany R. Fibrin deposition in primary and metastatic human brain tumours. Blood Coagul Fibrinolysis. 1996; 7:536). Indeed, many significant hemostatic abnormalities have been described in patients with cancer, including disseminated intravascular coagulation, hemorrhagic events, and migratory thrombophlebitis. Hemostatic complications are a common cause of death in patients with cancer. Many tumor cells possess strong procoagulant activities that promote the local activation of the coagulation system. Tumor-mediated activation of the coagulation cascade has been implicated in both the formation of tumor stroma and the promotion of hematogenous metastasis. Fibrin matrix, moreover, is known to promote the migration of a substantial number of distinct cell types, including both transformed cells, macrophages, and fibroblasts. In particular, much like in a healing wound, the deposition of fibrin/fibrinogen, along with other adhesive glycoproteins, into the extracellular matrix (ECM) have been shown to serve as a scaffold to support binding of growth factors and to promote the cellular responses of adhesion, proliferation, and migration during angiogenesis and tumor cell growth (see, for instance: Dvorak H F, Nagy J A, Berse B, et al. Vascular permeability factor, fibrin, and the pathogenesis of tumor stroma formation, Ann N Y Acad. Sci. 1992; 667:101; Rickles F R, Patierno S, Fernandez P M. Tissue Factor, Thrombin, and Cancer. Chest. 2003; 124:58 S-68S; Brown H F, Van der Water L, Hervey V S, Dvorak H F. Fibrinogen influx and accumulation of cross-linked fibrin in healing wounds and in tumor stroma. Am J Pathol. 1988; 130:4559; Dvorak H F, Hervey V S, Estrella P, Brown L F, Mc-Donagh J, Dvorak A M. Fibrin containing gels induce angiogenesis: implication for tumor stroma generation and wound healing. Lab Invest. 1987; 57:673 and Rickles F R, Patierno S, Fernandez P M. Tissue Factor, Thrombin and Cancer. Cest. 2003; 124:58 S-68S). Most solid tumors in humans contain considerable amounts of cross-linked fibrin, suggesting that it is important in tumor stroma formation. Studies indicate that both fibrinogen and fibrin localize at the tumor-host cell interface (see, for instance: Rickles F R, Patierno S, Fernandez P M. Tissue Factor, Thrombin and Cancer. Cest. 2003; 124:58 S-68S; Costantini V, Zacharski L R, Memoli V A et al. Fibrinogen deposition without thrombin generation in primary human breast cancer. Cancer Res. 1991; 51: 349-353 and Simpson-Haidaris P J and Rybarczyky B. Tumors and Fibrinogen: The Role of Fibrinogen as an Extracellular Matrix Protein. Ann. N.Y. Acad. Sci., 2001 936(1): 406-425). Fibrin matrices promote neovascularization, supporting the notion that fibrin may facilitate tumor stroma formation by mechanisms that are analogous to wound repair.
Moreover, a correlation seems to exist between plasma fibrinogen levels and tumor size, depth of tumor invasion and metastasis (See, for instance, Lee J H, Ryu K W, Kim S, Bae J M. Preoperative plasma fibrinogen levels in gastric cancer patients correlate with extent of tumor. Hepatogastroenterology 2004; 51:1860-3). In addition, it is known that fibrin/platelets are involved in protecting tumor cells from the action of the circulating natural killers units provided by human immune system thus improving the survival of circulating tumor (See, for instance, Palumbo J S, et al. platelets and fibrin(ogen) increase metastatic potential by impeding natural killer cell-mediated elimination of tumor cells. Blood, 2005; 105:178). This implies, for example, that a conventional tumor therapy using antibodies that target tumors may not effectively treat tumors containing fibrin because these tumor are protected by fibrin.
Thus, visualization of fibrin deposition and targeted inhibition/destruction of established vasculature and clotted fibrin is considered an important tool against malignant disease progression. Consequently, there remains a need for improved fibrin-binding compounds for use in sensitive diagnosis and specific therapy of pathological conditions associated with fibrin deposition, and, particularly, of solid tumors.
Fibrin also has been implicated in angiogenic processes. In a developing embryo, the primary vascular network is established by in situ differentiation of meso-dermal cells in a process called vasculogenesis. After embryonic vasculogenesis it is believed that all subsequent generation of new blood vessels, in the embryo or in adults, is governed by the sprouting or splitting of new capillaries from the pre-existing vasculature in a process called angiogenesis (Pepper, M. et al., 1996. Enzyme Protein, 49:138-162; Risau, W., 1997. Nature, 386:671-674). Angiogenesis is not only involved in embryonic development and normal tissue growth and repair, it is also involved in the female reproductive cycle, establishment and maintenance of pregnancy, and in repair of wounds and fractures.
In addition to normal angiogenic processes, angiogenic events also are involved in a number of important pathological processes, notably tumor growth and metastasis, and other conditions in which blood vessel proliferation is increased, such as diabetic retinopathy, psoriasis, arthropathies and rheumatoid arthritis. Indeed, angiogenesis is so important in the transition of a tumor from hyperplastic to neoplastic growth, that inhibition of angiogenesis has shown promise as a cancer therapy (Kim, K. et al., 1993. Nature, 362:841-844). In these pathological processes, fibrin provides the structural mesh required for the generation of new blood vessels.
There is a need, therefore, for sensitive and effective assays to detect the presence of fibrin and fibrin-associated diseases. More specifically there is a need for non-invasive reagents that can specifically bind fibrin and can be used to detect pathological thrombic conditions as well as conditions associated with pathological angiogenic processes.